A NIRS-Based Technique for Monitoring Brain Tissue Oxygenation in Stroke Patients

Abstract

Stroke is a global health issue caused by reduced blood flow to the brain, which leads to severe motor disabilities. Measuring oxygen levels in the brain tissue is crucial for understanding the severity and evolution of stroke. While CT or fMRI scans are preferred for confirming a stroke due to their high sensitivity, Near-Infrared Spectroscopy (NIRS)-based systems could be an alternative for monitoring stroke evolution. This study explores the potential of fNIRS signals to assess brain tissue in chronic stroke patients along with rehabilitation therapy. To study the feasibility of this proposal, ten healthy subjects and three stroke patients participated. For signal acquisition, two NIRS sensors were placed on the forehead of the subjects, who were asked to remain in a resting state for 5 min, followed by a 30 s motor task for each hand, which consists of opening and closing the hand at a steady pace, with a 1 min rest period in between. Acomplete protocol for placing sensors and a signal processing algorithm are proposed. In healthy subjects, a measurable change in oxygen saturation was found, with statistically significant differences (females p = 0.016, males p = 0.005) between the resting-state and the hand movement conditions. This work showed the feasibility of the complete proposal, including the NIRS sensor, the placement, the tasks protocol, and signal processing, for monitoring the state of the brain tissue cerebral oxygenation in stroke patients undergoing rehabilitation therapy. Thus this is a non-invasive barin assessment test based on fNIRS with the potential to be implemented in non-controlled clinical environments.

Keywords: deoxyhemoglobin; fNIRS; oxyhemoglobin; reflected-light; rehabilitation.

Figure 1

NIRS sensor placement.

Figure 2

Methodology proposal comprising the NIRS sensors placement, the rest/movement task signal acquisition protocol, and its processing to obtain brain tissue oxyhemoglobin and deoxyhemoglobin concentrations.

Figure 3

Oxygen saturation signals. The AC and DC components are shown. The segments that represent a heartbeat are also present as systole, diastole, and peak. (a) Reflected red light, signal λ1. (b) Reflected infrared light, signal λ2.

Figure 4

Brain SpO₂ variation is observed in a healthy subject. The time segments that correspond to rest and right- and left-hand movement can be seen in light gray, orange, and blue, respectively. (a) NIRS left channel. (b) NIRS right channel.

Figure 5

Concentrations of the chromophores for oxygenated (HbO₂) and deoxygenated (HHb) hemoglobin for a healthy subject. The gray area corresponds to the rest state, the light orange area corresponds to the right-hand movement, and the light blue area corresponds to the left-hand movement. (a) NIRS left channel. (b) NIRS right channel.

Figure 6

Concentrations of the chromophores for oxygenated (HbO₂) and deoxygenated (HHb) hemoglobin for stroke patient 1. The gray area corresponds to the rest state, the light orange area corresponds to the right-hand movement, and the light blue area corresponds to the left-hand movement. (a) Oxygen saturation NIRS left channel. (b) Oxygen saturation NIRS right channel. (c) Concentration changes during rest and hand activation, NIRS left channel. (d) Concentration changes during rest and hand activation, NIRS right channel.

Figure 6

Concentrations of the chromophores for oxygenated (HbO₂) and deoxygenated (HHb) hemoglobin for stroke patient 1. The gray area corresponds to the rest state, the light orange area corresponds to the right-hand movement, and the light blue area corresponds to the left-hand movement. (a) Oxygen saturation NIRS left channel. (b) Oxygen saturation NIRS right channel. (c) Concentration changes during rest and hand activation, NIRS left channel. (d) Concentration changes during rest and hand activation, NIRS right channel.